Tubular screen

ABSTRACT

A tubular screen means formed by the helical winding and attachment of a continuous rod member around a plurality of spaced longitudinal bar members in a manner sufficient to provide a continuous helical slot opening of continuously increasing slot width.

United States Patent Inventor David M. Boyd Clarendon Hills, 111.

Dec. 30, 1968 June 15, 1971 Universal 011 Products Company Des Plalnes, Ill.

Appl. No. Filed Patented Assignee TUBULAR SCREEN 5 Claims, 9 Drawing Figs.

US. Cl 166/231, 210/497.1 int. Cl B0ld 29/10 Field ofSearch 210/497.1

References Cited UNITED STATES PATENTS 7/1904 King 210/497.1 6/1937 Chorlton. 210/497.1X 7/1936 Johnson 2l0/497.1X 4/1944 Bennison.. 210/497.1X 1/1952 Layte 210/497.1X 6/1954 Banchback.. 2l0/497.1X 12/1969 Fournier 210/4971 Primary Examiner-David H. Brown Attorneys-James R. Hoatson, Jr. and Joseph C. Mason, Jr.

ABSTRACT: A tubular screen means formed by the helical winding and attachment of a continuous rod member around a plurality of spaced longitudinal bar members in a manner sufficient to provide a continuous helical slot opening of continuously increasing slot width.

PATENTEU JUN] 512m SHEET 1 OF 3 BED A BNVENTORI BED C c: 1: ZZ'JILLLL BED [D PATENTED JUN] 5 l9?! SHEET 2 BF 3 I ML BNVENTOR: 0mm M. aovo ATTORNEYS TUBULAR SCREEN BACKGROUND OF THE INVENTION The present invention relates to a novel tubular screen means of the general type described in U.S. Pat. Nos. 2,046,456; 2,046,457; 2,046,458; 2,046,459; 2,046,460; 2,046,46l;and 3,101,526.

In general, these patents relate to rust-proof metallic water well screens of a cylindrical shape which comprise a mu]- tiplicity of longitudinal extending bars or rods held in spaced parallel relation by a continuous rod member which is joined to the longitudinal bar members at each crossing point by welded joints. The spacing of the turns of the continuous rod member determines a helical slot width which is held uniformly within small tolerances for efficient screen performance.

' The method of fabrication for such tubular screens is set forth in the above patents. In general, the metallic screen means is fabricated by rotating a substantially cylindrical group of longitudinal bar members about its longitudinal axis. Simultaneously, a continuous rod member is fed substantially tangentially to the group of longitudinal bar members. The continuous rod member is fused to each longitudinal bar member at the point of contact, typically by electrical resistance welding, while rotating the group of-bar members as a unit about its axis and simultaneously advancing the unit longitudinally at a constant rate of speed. In this manner, the continuous rod member is helically wound around the longitudinal bar members and simultaneously fused thereto in a manner sufficient to provide a helical slot opening between adjacent helical coils of the continuous rod member, and thereby provide a continuous helical slot opening of uniform width.

As noted hereinabove, the preferred utility of such tubular screens is in water wells since they have the advantage of a high structural strength in combination with a high fluid capacity while retaining the particulated solids within the water-containing geological formation. The tubular screen is provided with a helical slot opening of uniform width which is sufficient to prevent the passage of the sand or gravel contained in the geological formation.

More recently, such tubular screens have found other com- .mercial applications. The screen device described hereinabove is now employed as a filter insert in many applications where the removal of traces of particulated solids from a flowing liquid stream is required. The tubular screen also finds application in the sizing of particulated solids. Thus, a plurality of various screen sizes may be provided to retain oversized solids through the slot openings of predetennined uniform width.

In summary then, the screens of the type herein described have consistently been fabricated with a uniform slot opening.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a tubular screen means comprising a perforated longitudinal section having perforations providing greater open area with respect to increasing distance along the longitudinal axis.

It is a more particular object of the present invention to provide a tubular screen means formed by the helical winding and attachment of a continuous rod member around a plurality of spaced longitudinal bar members in a manner sufficient to provide a continuous helical slot opening of continuously increasing slot width.

The method of fabricating the inventive tubular screen means is very similar to the method set forth hereinabove. A substantially cylindrical group of longitudinal bar members is rotated about its longitudinal axis. The continuous rod member is simultaneously fed substantially tangentially to the group of longitudinal bar members and fused to each longitudinal bar member at the point of contact while rbtating the ,group of bar members as a unit about its axis. Simultaneously,

the unit is advanced longitudinally at a continuously increasing rate of speed, in contradistinction. to the prior art method of advancing the unit at a constant rate of speed. In this manner, the adjacent helical turns or coils of the continuous rod member become fused to the longitudinal bar members at a continuously increasing distance apart, thus providing a tubular screen means having a helical slot opening of continuously expanding helical slot width.

The inventive screen means may also be fabricated by advancing the rotating unit comprising the longitudinal bar members and the continuous rod member, at a very high initial rate of speed while continuously decreasing the longitudinal rate of speed at which the unit is advanced. In this manner of fabrication, the adjacent helical turns or coils of the continuous rod memberwould become fused to each longitudinal bar member at a continuously decreasing distance apart, thus providing a tubular screen means having a helical slot opening of continuously decreasing helical slot width.

Those skilled in the art can, of counse, perceive that when a tubular screen of continuously decreasing helical slot width is viewed from the opposite end it will be seen as a tubular screen of continuously increasing slot width. Thus, the inventive tubular screen means of the present invention will have a continuously and unidirectionally varying slot width which, depending upon the point of reference from which viewed, may be a continuously increasing slot width or a continuously decreasing slot width.

In summary then, the present invention may be characterized as a tubular screen means formed by the helical winding and attachment of a continuous rod member around a plurality of spaced longitudinal bar members in a manner sufficient to provide a continuous helical slot opening of continuously and unidirectionally varying slot width.

Additionally, the present invention may be characterized as a process for fabricating a tubular screen means which comprises rotating a substantially cylindrical group of longitudinal bar members about its longitudinal axis; simultaneously feeding a continuous rod member substantially tangentially to the group of longitudinal bar members; and fusing the continuous rod member to each longitudinal bar member at the point of contact, while rotating the group of longitudinal bars as a unit about its axis, and simultaneously advancing the unit longitudinally at a continuously increasing rate of speed, whereby adjacent helical coils of the continuous rod member become fused a continuously increasing distance apart on the longitudinal bar members.

Furthermore, the present invention may be characterized as a process for fabricating a tubular screen means which comprises, rotating a substantially cylindrical group of longitudinal bar members about its longitudinal axis; simultaneously feeding a continuous rod member substantially tangentially to the group of longitudinal bar members; and, fusing the continuous rod member to each longitudinal bar member at the point of contact, while rotating the group of longitudinal bars as a unit about its axis, and simultaneously advancing the unit longitudinally at a continuously decreasing rate of speed whereby adjacent helical coils of the continuous rod member become fused a continuously decreasing distance apart on the longitudinal bar members.

Those skilled in the art will realize that the inventive screen means herein described may not necessarily find utility as a fluid-solids screen, a fluid-solids filter, or a solid sizing apparatus in the prior art manner of operation, since the helical slot opening is not of uniform width.

However, the screen means of the present invention having a continuously expanding helical slot width may find utility as a liquid overflow weir or darn for retention of a liquid in a liquid reservoir. For example, the inventive tubular screen means may be employed as a novel fluid downcomer means which provides for retention of a liquid inventory upon a fluid distributing deck in a fluid contacting zone such as a reaction zone, an adsorption zone, an extraction zone, etc.

. The construction and configuration of the inventive screen means, as well as its utility, may be more clearly understood by now referring to the accompanying figures.

DESCRIPTION OF THE FIGURES FIG. I is a partially cut away elevational view indicating a typical hydrocarbon hydrocracking reactor vessel wherein the inventive tubular screen means is employed as the fluid downcomer of the catalyst support and fluid distribution deck contained therein.

FIG. 2 indicates a partially cut away elevational view of the downcomer means which comprises the inventive tubular screen means which is formed by the helical winding and attachment of a continuous helical slot opening of continuously increasing slot width.

FIG. 3 is a sectional plan view indicating the manner of construction of the downcomer means of FIG. 2 as indicated by lines 3-3 of FIG. 2.

FIGS. 4A through 4C indicate partial sectional views of the continuous rod members and longitudinal members of the downcomer means of FIGS. 2 and 3, showing various crosssectional configurations for the rod members. FIG. 5 comprises a graph which illustrates the advantages or effectiveness of fluid flow through the inventive screen means when utilized as the downcomer of a fluid distributing deck.

FIG. 6 provides a sectional elevation of a portion of the inventive screen means, and illustrates a further embodiment thereof.

FIG. 7 indicates a partial sectional view of the continuous rod member and a longitudinal bar member for the tubular screen of FIG. 6, showing an alternate cross-sectional configuration for the rod member.

Among the most important of the various commercial chemical processes are those involving the physical or chemical treatment of hydrocarbons and other organic materials with bodies of granular or particulated solid contact materials. Many of these processes involve the contacting of two fluids with the contacting material, and often the two fluids will comprise a liquid phase and a gas or vapor phase. It has been the experience in the art that the introduction of such mixtures of liquid and vapor into a bed of particulated contact solids in a uniformly distributed manner is difficult to achieve.

Typical of the art wherein uniform distribution of liquid and gas phases is necessary but infrequently achieved, is that of catalytic hydrocracking of various hydrocarbon oils. It is well known that the feed to such a reaction zone comprises liquid hydrocarbon, vaporized hydrocarbon, and a hydrogen-rich gas, and that this feed is introduced into the reaction zone at an elevated temperature. It is further known that the reactions which are encountered in this catalytic environment are exothermic, and that the temperature of the vapor phase and of the liquid hydrocarbon phase is increased due to the exothermic heat of reaction. In order to avoid excessive temperature within the catalyst bed it is, therefore, typical to arrange the catalyst in a plurality of separate superimposed fixed beds so that diluent or quench vapors may be distributed between the beds during the reaction. The cool quench vapors, normally comprising hydrogen-rich gas, reduce the temperature of the effluent from the bed above before the liquid-vapor mixture of hydrocarbon and hydrogen is fed into the bed of catalyst below.

It is typical in the art to support each individual bed of catalyst upon a perforated support plate. It is also typical in the art to introduce the quench hydrogen between the fixed beds of catalyst by means of a perforated pipe grid or other means which is positioned throughout the cross section of the reactor vessel at the quench point. The effluent from the catalyst bed above, thus rains down from the perforated support plate throughout the cross-sectional area of the reactor while the quench hydrogen is distributed by the perforated grid throughout the cross-sectional area of the reactor.

Referring now to FIG. I, there is shown in partially cut away elevation, a typical hydrocarbon hydrocracking reactor vessel containing four catalyst beds, and comprising a vertically elongated shell 1 containing an upper fluid port 2 for the introduction of feed material and a lower fluid port 3 for the discharge of reactor effluent. In addition, there is provided a fluid port 4 below each of the first three catalyst beds A, B, and C, whereby quench hydrogen may be introduced into the hot effluent passing into beds B, C, and D from the catalyst bed above.

Each catalyst bed contains particulated or granulated hydrocracking catalyst material 5 which may be present in pilled, spherical, or extruded form. The bed of catalyst is supported upon inert support material 6 which typically comprises ceramic balls, Raschig Rings, Berl Saddles, or any other inert support materials which are well known to those skilled in the art. The top of each catalyst bed contains a layer 7 of the same support material. As is well known to those skilled in the art, this top layer of material provides a method of enhancing distribution of fluid into the bed of catalyst particles 5 below, while simultaneously weighing down the bed of catalyst particles so that it may not be dislodged by any fluctuations or sudden surges of pressure.

Each catalyst bed comprising catalyst particles 5, inert support layer 6, and inert support layer 7 is held and retained upon the catalyst support and fluid distributing deck which comprises a substantially imperforate support plate 8 containing a plurality of fluid openings 9. Encompassing each fluid opening 9 and rising a finite distance above the face of support plate 8 there is provided a downcomer conduit 10 which is capped by an imperforated plate or other means 11. The downcomer conduit 10 is provided with perforations which are sufficient to allow the flow of fluid therethrough while retaining the particulated solids of the catalyst bed supported above.

Between each catalyst bed there is a void space 12 which is confined between the support plate 8 of the catalyst support and fluid distributing deck and the layer of inert support material 7 of the bed below. Into this open space there projects a hydrogen quench means 13. Typically, hydrogen quench means 13 will comprise a pipe grid or other conduit means having perforations 14 located directly below each fluid opening 9 in order to provide for a direct and intimate contact between the hot effluent mixture of liquid and vapor and the relatively cool quench hydrogen gas.

By providing the imperforate support plate 8 in combination with the perforated downcomers 10, the fluid distributing deck provides that liquid channelling down from the catalyst bed above will be retained on the deck in a liquid reservoir with a sufficient retention time to allow mixing of heavier viscous liquids which normally channel along the walls of chamber 1, with the lighter relatively nonviscous liquids which tend to channel throughout the central regions of the catalyst bed. As the liquids collect upon the distributor deck 8 they achieve an equilibrium liquid level due to pressure drop through the openings of perforate downcomer 10. The liquid will flow through the lower perforations of the downcomer due to liquid head while the vaporized hydrocarbon and reactant hydrogen of the gaseous-vapor phase will pass through the perforations in downcomer 10 which are above the liquid level.

As the effluent mixture of liquid and vapor passes through fluid opening 9, it meets the cold quench hydrogen which is discharged from perforations 14 in quench grid 13 directly below fluid opening 9. Thus, there is provided an opportunity for a direct contact of hot effluent and cold quench so that the resulting mixture will pass into the catalyst bed below at a substantially cooler and uniform temperature and in a substantially unifonn mixture of heavy hydrocarbon liquids, light hydrocarbon liquids, vaporized hydrocarbon, and hydrogen gas. This relatively uniform mixture thus is discharged substantially uniformly into the cross-sectional area of the catalyst bed below.

As noted in the summary of the invention as disclosed hereinabove, downcomer comprises a perforated longitudinal conduit having perforations providing greater open area with respect to increasing distance from the imperforate support plate 8. Thus, as the charge rate to the catalytic reactor 1 is reduced, the liquid level retained upon imperforate support plate 8 will tend to fall. However, as the level falls the area of the perforations which are available for liquid flow decreases, thereby providing that a reservoir of liquid will always be retained upon support plate 8 so that the liquids which channel down from the catalyst bed above are afforded sufficient time for mixing before they pass into the catalyst bed below. Similarly, if the charge rate of materials to the reactor vessel of FIG. 1 is increased, the liquid inventory retained upon imperforate support plate 8 will rise to a greater depth. As the liquid level rises, however, the open area provided by the perforations in the downcomers 10 increases with increasing height, thus allowing a greater flow of fluid therethrough as the liquid level seeks a higher height.

FIG. 2 illustrates a particularly preferred perforated downcomer for use in the fluid distributing deck. The downcomer means illustrated in FIG. 2 comprises the inventive tubular screen means which is formed by the helical winding and attachment of a continuous rod member around a plurality of spaced longitudinal bar members in a manner sufficient to provide a continuous helical slot opening of continuously increasing slot width. For screens of this general type, reference has previously been made to existing U.S. Patents. As will also be noted in connection with the cited patents, a preferable form of screen makes use of triangular or wedgeshaped rod members in the helical winding step so that selfcleaning" types of cylindrical screens will be formed. This selfcleaning characteristic will be more fully discussed hereinafter.

Referring now to FIG. 2, there is shown in partially cut away elevation, the imperforate support plate 8 of the fluid distributing deck and a typical fluid opening 9. The inventive tubular screen means which constitutes the downcomer ll) of FIG. 1 is covered by an imperforate plate 11. The tubular screen means is formed by the continuous helical winding of the continuous rod member 22 around the plurality of spaced longitudinal bar members 21, which are spaced in a circular tubular configuration in this embodiment. The helical winding of rod member 22 produces a continuous slot 23 between adjacent coils of the helically wound rod member 22. As the continuous rod member 22 is helically wound around the longitudinal bar members, it is continually attached or fused thereto, preferable by electrical resistance so as to provide spot welding of the touching rod member 22 to the longitudinal bar members 21. The result is a structurally strong tied together cylindrical fonn screen section containing fluid openings 24 which are formed by the sectioning of the helical slot opening 23 by the longitudinal bar members 21.

FIG. 3 is a sectional plan view of the inventive tubular screen means of FIG. 2 which is taken along line 3-3 in FIG. 2. FIG. 3 shows the imperforate support plate 8 and the fluid opening 9. There is also shown the longitudinal bar members 21 spaced in a circular configuration with continuous rod member 22 helically wound around and attached thereto. While the spacing of the longitudinal bar members 21 is preferably in a circular configuration, the tubular screen may also be formed by winding the continuous rod member and attaching it to bar members spaced in an elliptical or oval configuration.

Again, referring to FIG. 2, a close inspection thereof clearly indicates that the slot opening 23 is very narrow adjacent to imperforate support plate 8. However, the slot opening 23 increases with increasing height of the tubular screen means. This is accomplished by winding the continuous rod member 22 around the longitudinal bar members 21 in a continuous helix which has an increasingly wider spread between adjacent turns of the rod member. In this manner, there is provided a continuous helical slot opening 23 of continuously increasing slot width. The net result is that the fluid openings 24 which are confined between continuous rod member 22 and longitudinal bar members 21 provide a greater open area for fluid flow with respect to increasing distance from the face of imperforate support plate 8.

Thus, those skilled in the art will readily ascertain that as the liquid level builds upon the fluid distributing deck 8, the fluid openings 24 which are exposed to liquid and available for fluid flow therethrough, provide an increasing open area for fluid flow as the height of liquid on imperforate support plate 8 increases. Thus, if the throughput in the reactor of FIG. I is increased, the liquid level will rise higher and be exposed to greater sized fluid openings 24 at the higher liquid level. Thus, the increased flow rate is easily handled through the downcomers 10 without a large increase in pressure drop through the reactor vessel. As the throughput to the reactor of FIG. 2 is decreased, the liquid level falls and is exposed to fluid opening 24 of lesser area, thus providing that some liquid will always be retained in a liquid reservoir on imperforate support plate 8.

Referring now to FIGS. 4A through 4C, there is shown partial sectional views through the continuous rod member 22 showing various cross sections of the rod member. Thus, in FIG. 4A, there is shown longitudinal bar member 21 and continuous rod member 22 having a circular cross-sectional area. It will be noted that the cross section of the slot has a converging configuration in the direction of flluid flow so that the slot becomes narrower at the diameters of adjacent turns of helical coils of rod member 22. Thus, any particulated solid such as catalyst fines may become lodged in slot 23 and blind a portion of the tubular screen downcomer.

It is, therefore, a preferred embodiment that the continuous rod member 22 have a triangular or wedge-shaped cross section as shown in FIGS. 43 and 4C. By having the wider portion of the wedge-shaped cross section of rod member 22 along the outside surface of the screen, the slot opening 23 is thereby provided with an increasing sized fluid passageway for flow of fluid, and once any entrained particulated matter such as catalyst fines passes into the slot opening 23 it can more readily pass outward toward the inside of the screen. It will be seen in FIG. 4B and in FIG. 4C that the slot opening 23 also results in a triangular or wedge-shaped cross section for this fluid passageway, with the widest portion of the wedge-shaped slot opening toward the inside surface of the screen. Thus, by employing the triangular or wedge-shaped cross-sectional configuration for the rod member 22, the tubular screen of FIG. 2 is a self-cleaning-type screen" since retention of solids and blinding of the screen is minimized.

FIG. 4B specifically illustrates the cross-sectional area of rod member 22 having a solid trapezoidal shape. FIG. 4C illustrates a channel-type cross section wherein the open end of the channel is narrower than the flange end of the channel, thereby providing the desired wedge shape. This channel type of continuous rod member is more particularly discussed and illustrated in U.S. Pat. No. 3,101,526 previously cited.

FIG. 5 illustrates test results which show the effectiveness of the inventive fluid distributing deck for retaining an inventory of liquid at varying flow rate.

Tests were run utilizing four downcomers which were fabricated by winding a continuous rod member over longitudinal bar members to produce a screen of the type shown in FIG. 2. The continuous rod member had wedge-shaped crosssectional area as illustrated in FIG. 48 with the wide part of the wedge on the outer screen surface having a width of one sixteenth of an inch. All four screens were 2 inches in outside diameter and provided a downcomer height of 8 inches. However, the first three screens were fabricated in the typical prior art manner with uniform and constant helical slot widths of 0.003 inches, 0.010 inches, and 0.030 inches. The fourth screen was a screen of the present invention having a continuously expanding helical slot width of the type which has been disclosed with particularly in reference to FIG. 2. This fourth screen had a slot opening 0.003 inches at the bottom of the tubular screen downcomer and the continuously expanding helical slot opening had a width of 0.030 inches at the top of the tubular screen downcomer.

Capacity tests for the four downcomers were individually made using water in ambient air and the results are shown in FIG. wherein there is plotted height of liquid versus rate of flow. While the tests were not in an environment of hydrocarbon and hydrogen gas at elevated temperature and pressure,

' the results are qualitatively indicative of the effectiveness of operation of the inventive distributing deck in any environment.

Referring now to FIG. 5, it is seen that inches of liquid head is plotted against gallons per minute (gpm) of liquid flow. Note that at the low flow rates, the down comers having 0.003 inch and 0.010 inch slot openings retain a high liquid level on the deck. Thus, in operation in a hydrocracking reactor of the type shown in FIG. 1, liquids channelling down from the catalyst beds above would have a relatively high residence time and would be afforded ample opportunity to interm ix before passing down into the catalyst bed below via the downcomer. However, it will be seen that for these small slot openings, the total throughput for these downcomer screens is limited. Thus, at the total immersion of the downcomer at 8 inches of liquid head, the slotted screen having the 0.003 inch helical slot can only pass about gpm while the downcomer having the 0.010 inch helical slot can only pass about 40 gpm. It will be seen that the downcomer having the helical slot of 0.030 inches can readily pass a high rate of liquid flow. However, at a low flow rate, this downcomer will only retain a small liquid head on the fluid distributing deck, thus providing a low residence time and minimizing effective mixing of fluids which may channel down from the catalyst bed above. The advantage of the 0.030 inch slot opening downcomer is that is affords high liquid throughput without covering the total downcomer height with liquid, so that it still contains slot openings above the liquid level for the passage of vapor flow.

However, the fourth downcomer comprising the inventive tubular screen means having the continuously expanding helical slot opening, combines the advantages and eliminates the disadvantages of the first three downcomer devices tested. By

referring to FIG. 5, it will be seen that at low flow rates the downcomer with the continuously expanding slot opening is capable of retaining a high liquid level on the distributing deck, thus affording a high residence time and ample opportunity for mixing of the liquids which channel down from the catalyst bed above. As the throughput increases, however, since the helical slot is expanding in a continuous manner to expose a greater fluid opening through the tubular screen downcomer, the rate of flow through the downcomer increases greatly while the liquid level is increased only moderately. Thus, the downcomer comprising the inventive tubular screen with the continuously expanding helical slot opening is capable of passing a high rate of liquid flow while still retaining a sufficient amount of screen opening exposed to the vapor phase for vapor flow therethrough.

In the embodiment which has been discussed hereinabove in relation to FIGS. 1 through 5, the flow of fluid passes from the outside of the screen to the inside of the screen. Those skilled in the art will realize that the inventive tubular screen may also find application where the fluid flow passes from the inside of the screen to the outside of the screen. Such an alternate embodiment is shown in FIG. 6, wherein a portion of such a tubular screen is shown in sectional elevation. Referring to FIG. 6, there is shown the continuous rod member 22 which is helically wound around a plurality of longitudinal bar members 21 to form a plurality of fluid openings 24. The rod member 22 has the preferred wedge-shaped cross section with the wider portion thereof on the inner screen surface. Therefore, this alternate embodiment of the tubular screen has a continuously expanding helical slot opening 23 of wedgeshaped cross section having the wider portion thereof at the outside screen surface. Thus, the tubular screen ofthe present invention still retains its self-cleaning characteristics when the flow of fluid is from the inside screen surface to the outside screen surface.

This self-cleaning aspect of the tubular screen of FIG. 6 is seen more clearly in FIG. 7, wherein there is shown a partial sectional view of an alternate construction for the screen of FIG. 6. The cross section of the continuous rod member 22 is a solid wedge in FIG. 6, while rod member 22 has a channel cross section in FIG. 7. In either cross-sectional configuration, the continuous rod member 22 has a wedge-shaped cross section, with the wider portion of the wedge at the inner screen surface. This results in a continuous helical slot opening 23 which provides a fluid passageway of increasing size as the fluid flows from the inside of the screen to the outside of the screen. Thus, as can be clearly seen from the illustration of FIG. 7, any particulated matter which passes into the slot opening 23 will not blind the screen, since it can easily pass through the wedge-shaped slot opening 23 and be discharged from the tubular screen at the outside screen surface.

PREFERRED EMBODIMENTS Those skilled in the art will readily ascertain the utility of the inventive tubular screen means and its advantages. In particular, the inventive screen means provides flexibility of operation at various fluid flow rates, and in the particular embodiment illustrated hereinabove, it also provides a means for retaining particulated solids while having a high fluid capacity.

While the foregoing disclosure has been relative to the inventive tubular screen fabricated from a rust resistant or a corrosion resistant metal, those skilled in the art will realize that the present invention is not so limited. The inventive tubular screen may be fabricated from many types of materials including plastics, fiberglass, copper, brass, stainless steel, various metallic alloys. and so forth. In addition, it will be realized that the inventive screen is not limited to the dimensions which have been disclosed hereinabove. Screen of the present invention may have diameters of from 1 to 2 inches or diameters as large as several feet. Similarly,the length of the inventive tubular screen is not limited. In addition, the continuously expanding helical slot opening may vary from as little as 0.001 inch to as much as one-fourth inch or even more along the length of the tubular screen. The dimensional design and material of construction for the inventive screen will, of course, depend upon the specific environment wherein it is utilized.

Among the design considerations are the type of fluids which pass through the screen, the fluid flow rate, and the pressure drop which can be tolerated within the environment wherein the inventive screen is used. Thus, in the illustrative embodiment hereinabove, hydrocarbon liquid and hydrogenrich gas were passed through the inventive tubular screen. To size the screen for such an application one must consider the flow rates of the liquid and vapor phases and the flowing density of each phase. Additionally, the molecular weight of the flowing fluids must be considered as well as the temperature and pressure of the environment wherein the tubular screen of the present invention is utilized.

Those skilled in the art will readily ascertain that the inventive screen is not limited to the fluids which have been noted for illustrative purposes hereinabove. While the preceding disclosure has been directed to the passage of a liquid phase and a vapor phase through the screen, it must be realized that the screen will function with equal effectiveness in a liquid-liquid environment. Thus, the screen may have application in holding an interfacial level between two liquid phases in a liquidliquid contacting system such as in an extraction zone. Thus, if downcomer 10 were oriented to rise to a height above support plate 8 as shown in the figures and discussed hereinabove, the height of heavy liquid phase accumulated below a light liquid phase upon plate 8 would be effected by liquid flow rates in a manner which has been described hereinabove, in relation to the accumulation of a hydrocarbon liquid below a hydrogenrich vapor phase. If the apparatus were inverted, however, so

that downcomer 10 extended to a distance below support plate 8, then the increasing screen openings of increasing dimension with respect to increasing distance from the plate would function to adjust the height of light liquid phase confined below plate 8 and above the heavy liquid phase by functioning as an upcomer for the light liquid phase. The utility of the inventive tubular screen and the method of operation in such a liquid-liquid environment are readily ascertainable to those skilled in the art.

The manner of operation and the utility of the inventive tubular screen means, as well as its dimensional design, are readily ascertainable to those skilled in the art from the teachings which have been presented hereinabove and the advantages to be accrued from the inventive screen means are equally apparent.

Therefore, it may be summarized that a preferred embodiment of the present invention comprises a tubular screen means formed by the helical winding and attachment of a continuous rod member having wedge-shaped cross section around a plurality of spaced longitudinal bar members in a manner sufficient to provide a continuous helical slot opening of continuously increasing slot width having wedge-shaped cross section.

The invention I claim is:

1. A tubular screen means formed by the helical winding and attachment of a continuous rod member around a plurality of spaced longitudinal bar members in a manner sufiicient to provide a continuous helical slot opening of continuously and unidirectionally varying slot width.

2. Screen means of claim 1 wherein said continuous rod member is of wedge-shaped cross section with the wider portion thereof along the outer screen surface resulting in a helical slot opening having a wedge-shaped cross section with the wider portion thereof along the inner screen surface.

3. Screen means of claim 2 wherein said continuous rod member has a channel-shaped cross section.

4. Screen means of claim 1 wherein said continuous rod member is of wedge-shaped cross section with the wider portion thereof along the inner screen surface resulting in a helical slot opening having a wedge-shaped cross section with the wider portion thereof along the outer screen surface.

5. Screen means of claim 4 wherein said continuous rod member has a channel-shaped cross section. 

1. A tubular screen means formed by the helical winding and attachment of a continuous rod member around a plurality of spaced longitudinal bar members in a manner sufficient to provide a continuous helical slot opening of continuously and unidirectionally varying slot width.
 2. Screen means of claim 1 wherein said continuous rod member is of wedge-shaped cross section with the wider portion thereof along the outer screen surface resulting in a helical slot opening having a wedge-shaped cross section with the wider portion thereof along the inner screen surface.
 3. Screen means of claim 2 wherein said continuous rod member has a channel-shaped cross section.
 4. Screen means of claim 1 wherein said continuous rod member is of wedge-shaped cross section with the wider portion thereof along the inner screen surface resulting in a helical slot opening having a wedge-shaped cross section with the wider portion thereof along the outer screen surface.
 5. Screen means of claim 4 wherein said continuous rod member has a channel-shaped cross section. 